1. Field of the Invention
This invention relates to power input controls for motors, and particularly to a control which varies input power to an AC induction motor proportional to loading on the motor.
2. General Description of the Prior Art
The induction motor is perhaps the most rugged, and is certainly one of the most commonly used motors. It runs at an essentially constant speed which, within certain limits, is independent of both load and applied voltage. For efficient operation, the applied voltage should be a function of the load. Heretofore, this has not been practically accomplished. Line voltages are a matter of availability from a local utility. In the case of nominal 115-volt service, line voltage may be typically in the range of 105 to 125 volts and may not be constant with the service from a particular source and often varying significantly over a 24-hour period. In recognition of this, typically a 115-volt motor would be designed to deliver its rated load plus a safety margin at an under voltage condition of 105 to 110 volts. However, in taking care of the ability of the motor to perform its rated job at under voltage conditions, it becomes wasteful when line voltage is in the 120- to 125-volt range. Further, since this type of motor draws essentially the same current whether loaded or unloaded, motor efficiency goes down when less than a rated load is applied to the motor. Thus, where a user employs a motor over-rated for a job or a variable load is applied to the motor, efficiency suffers and waste of electrical power occurs. 3. Object of the Invention
It is the object of this invention to provide an electrical device which, when placed in circuit with the power input of an AC induction motor, will effect a reduction in power normally provided the motor when operated in either a condition where line voltage is greater than normal and/or motor loading is less than a rated load.